1. Field of the Invention
The present invention relates to a decoding device for decoding a bit stream defined by MPEG2 Multichannel, Layer II, for example, or decoding both a bit stream defined by MPEG2 Multichannel and a bit stream defined by MPEG1.
2. Description of the Related Art
Conventionally, in a decoding device for decoding a bit stream defined by MPEG2 Multichannel stipulated in ISO-IEC 13818-3.2, decoding of an MPEG2 multichannel extended area of a bit stream defined by MPEG2 Multichannel is begun only after decoding of an MPEG1 compatible area thereof is completed. Such a conventional MPEG2 multichannel decoding device is therefore required to secure a memory of at least [2.times.1152.times.(number of bytes given to one sample after reverse quantization)] bytes.
On the other hand, in a conventional decoding device for decoding both a bit stream defined by MPEG2 Multichannel and a bit stream defined by MPEG1, whether or not a bit stream is a bit stream defined by MPEG2 Multichannel is determined in the following manner. An MPEG2 multichannel determination method stipulated in ISO-IEC 13818-3, for example, uses cyclic redundancy check (CRC). According to this method, even if the bit stream is a bit stream defined by MPEG1 which does not include an MPEG2 multichannel extended area, decoding for multichannel streams is performed if the bit stream passes the CRC (error check). This causes erroneous operation.
Another problem is that, in a decoding method stipulated in ISO-IEC 13818-3, for example, decoding is continued even when a length of bit stream exceeding one frame length has been decoded. This also causes erroneous operation.
As described above, the conventional MPEG2 multichannel decoding device has a problem of requiring a buffer memory with large capacity, thereby increasing the size of the device.
The conventional decoding device which decodes both bit streams defined by MPEG2 Multichannel and MPEG1 also has a problem that decoding for MPEG2 multichannel streams is performed for an MPEG1 bit stream if the bit stream passes the CRC for MPEG2 multichannel streams, causing erroneous operation.
The object of the present invention is to provide a decoding device capable of decoding an MPEG2 multichannel bit stream using a buffer memory with a small capacity and determining correctly whether or not an MPEG2 multichannel extended area exists in a bit stream in the case where the decoding device decodes both bit streams defined by MPEG1 and MPEG2 Multichannel.